2018-03-20 02:52:45

by Sinan Kaya

Subject: [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on weakly-ordered archs

Code includes barrier() followed by writel(). writel() already has a
barrier
on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Since code already has an explicit barrier call, changing writeX() to
writeX_relaxed().

Signed-off-by: Sinan Kaya <[email protected]>
---
drivers/scsi/ipr.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index e07dd99..209adac 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -762,9 +762,9 @@ static void ipr_mask_and_clear_interrupts(struct ipr_ioa_cfg *ioa_cfg,

/* Set interrupt mask to stop all new interrupts */
if (ioa_cfg->sis64)
- writeq(~0, ioa_cfg->regs.set_interrupt_mask_reg);
+ writeq_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
else
- writel(~0, ioa_cfg->regs.set_interrupt_mask_reg);
+ writel_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);

/* Clear any pending interrupts */
if (ioa_cfg->sis64)
@@ -8435,7 +8435,8 @@ static int ipr_reset_enable_ioa(struct ipr_cmnd *ipr_cmd)
wmb();
if (ioa_cfg->sis64) {
/* Set the adapter to the correct endian mode. */
- writel(IPR_ENDIAN_SWAP_KEY, ioa_cfg->regs.endian_swap_reg);
+ writel_relaxed(IPR_ENDIAN_SWAP_KEY,
+ ioa_cfg->regs.endian_swap_reg);
int_reg = readl(ioa_cfg->regs.endian_swap_reg);
}

--
2.7.4

2018-05-29 20:48:12

by Brian King

Subject: Re: [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on weakly-ordered archs

On 03/19/2018 09:50 PM, Sinan Kaya wrote:
> Code includes barrier() followed by writel(). writel() already has a
> barrier
> on some architectures like arm64.
>
> This ends up CPU observing two barriers back to back before executing the
> register write.
>
> Since code already has an explicit barrier call, changing writeX() to
> writeX_relaxed().
>
> Signed-off-by: Sinan Kaya <[email protected]>
> ---
> drivers/scsi/ipr.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
> index e07dd99..209adac 100644
> --- a/drivers/scsi/ipr.c
> +++ b/drivers/scsi/ipr.c
> @@ -762,9 +762,9 @@ static void ipr_mask_and_clear_interrupts(struct ipr_ioa_cfg *ioa_cfg,
>
> /* Set interrupt mask to stop all new interrupts */
> if (ioa_cfg->sis64)
> - writeq(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> + writeq_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> else
> - writel(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> + writel_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
>
> /* Clear any pending interrupts */
> if (ioa_cfg->sis64)
> @@ -8435,7 +8435,8 @@ static int ipr_reset_enable_ioa(struct ipr_cmnd *ipr_cmd)
> wmb();
> if (ioa_cfg->sis64) {
> /* Set the adapter to the correct endian mode. */
> - writel(IPR_ENDIAN_SWAP_KEY, ioa_cfg->regs.endian_swap_reg);
> + writel_relaxed(IPR_ENDIAN_SWAP_KEY,
> + ioa_cfg->regs.endian_swap_reg);
> int_reg = readl(ioa_cfg->regs.endian_swap_reg);
> }
>

Looks fine to me. Thanks.

Acked-by: Brian King <[email protected]>

--
Brian King
Power Linux I/O
IBM Linux Technology Center